This invention relates to the suspension of an annular secondary structure on a primary structure, in particular of a stator structure acted upon by hot gas on a casing structure of a gas turbine, in the form of what may be referred to as a spoke-type centering device.
Spoke-type centering devices are used in order to suspend annular secondary structures centrically on mostly likewise annular or tubular primary structures. In this case, radial relative movements of the structures in relation to one another are to be possible essentially without constraining forces and deformations, while at the same time concentricity is maintained. The principle is appropriate, in particular, when widely differing thermal expansions of two concentric structures are to be compensated. If the secondary structure is relatively elastic, that is to say has low dimensional stability, it should be, as far as possible, stabilized and stiffened via the suspension.
German patent publication DE 198 07 247 C2 discloses a turbomachine with rotor and stator, which has at least one specially designed guide-vane ring. The latter is designed as a self-supporting component with a reinforcement on the inner shroud and with a segmented outer shroud. The guide-vane ring is positioned in the casing of the turbomachine via a spoke-type centering device having at least three xe2x80x9cspokesxe2x80x9d. The sliding guides of the spoke-type centering device have bearing journals in bearing bushes, and the linear direction of movement in each sliding guide runs radially with respect to the guide-vane ring and casing.
It is likewise customary to implement the sliding guides by way of sliding blocks running in straight grooves, the direction of movement running, as is usual, radially with respect to the coupled structures. Experience shows that pronounced wear often occurs on the sliding elements of conventional spoke-type centering devices. Permanent deformations of the thin-walled secondary structures have sometimes been detected. Both types of damage indicate that higher forces than should occur under ideally rotationally symmetrical conditions obviously arise in the guides. The cause is probably non-rotationally symmetrical expansion states of the structures, which, in gas turbines, may be brought about, in particular, by non-homogeneous gas temperature distributions. Especially where structures of large diameter are concerned, with a multiplicity of sliding guides, that is to say of xe2x80x9cspokesxe2x80x9d, the risk of the occurrence of high constraining forces increases. By virtue of geometry, the orientation of the direction of movement changes only slightly from guide to guide, so that, in the event of expansion of the secondary-structure region located between them, jamming may occur in both guides because of a fall below the angle of friction, with the result that free structure expansion becomes impossible. A further disadvantage of the conventional radial spoke-type centering devices is that these xe2x80x9csoftxe2x80x9d secondary structures are stiffened only when there is an odd number of sliding guides (xe2x80x9cspokesxe2x80x9d).
In view of these disadvantages of known spoke-type centering devices, one object of this invention is to find a suspension for an annular secondary structure on a primary structure in the manner of a spoke-type centering device having at least three differently oriented sliding guides. The suspension prevents or largely reduces the constraining forces and deformations, and also wear, and makes it possible to stiffen flexible secondary structures, irrespective of whether there is an even or odd number of sliding guides.
According to the invention, the linear direction of movement of each sliding guide is inclined at an angle xcex2 to the radial direction of the structures, so that the relative movement acquires a radial component and a tangential component. Guide jamming, with all its disadvantages, is thereby avoided with a high degree of reliability. This applies to homogeneous and non-homogeneous dimensional changes of the secondary structure. In the case of homogeneous rotationally symmetrical expansion or contraction of the secondary structure, the latter also executes a small relative rotation in relation to the primary structure for kinematic reasons, which in most cases is acceptable. In the case of non-homogeneous locally differing expansion or contraction of the secondary structure, the latter is deformed elastically to some extent away from the annular configuration. However, the sliding-guide forces resulting from this are substantially lower than during the jamming of a conventional radial spoke-type centering device. The dimensional deviations are likewise kept within acceptable limits. One effect of the invention, namely to increase dimensional stability, may permit the secondary structure to be designed to be more elastic and lighter than in a conventional spoke-type centering device.